Making a new “Star Wars” movie can be like gaining access to a toy collection that has been amassed over four decades. For the creators of “Rogue One,” a film designed as a narrative lead-in to the original “Star Wars,” it was a chance to play with characters, vehicles and locations sacred to this series.

But as they revisited the 1977 George Lucas movie that started the “Star Wars” franchise, and gave fresh screen time to some lesser-known heroes and villains, the staffs of Lucasfilm and Industrial Light & Magic faced artistic and technological hurdles: most prominently, using a combination of live action and digital effects to bring back the character Grand Moff Tarkin. This nefarious ally of Darth Vader and commander of the Death Star was played by Peter Cushing, the horror-film actor, who died in 1994.

In doing so, they also waded into a postmodern debate about the ethics of prolonging the life span of a character and his likeness beyond that of the actor who originated the role.

The effects experts and storytellers behind “Rogue One” (which was directed by Gareth Edwards and written by Chris Weitz and Tony Gilroy) say they have given careful thought to these issues and were guided by their reverence for this interstellar epic.

“A lot of us got into the industry because of ‘Star Wars,’ and we all have this love of the original source material,” said John Knoll, the chief creative officer at Industrial Light & Magic and a visual effects supervisor on “Rogue One” who shares story credit on the film with Gary Whitta. In his view, the character effects are “in the spirit of what a lot of ‘Star Wars’ has done in the past.”

Some vintage “Rogue One” characters were easier to conjure than others. General Dodonna, a rebel officer from the original “Star Wars” was simply recast; he was played by Alex McCrindle in the first film and Ian McElhinney in the new one.

Jimmy Smits, who played the galactic Senator Bail Organa in the “Star Wars” prequels, returned in that role. And Genevieve O’Reilly, who played the rebellion leader Mon Mothma in “Star Wars: Episode III — Revenge of the Sith,” only to have her footage cut from the film, finally got to appear as that character in “Rogue One.” (The role was originated by Caroline Blakiston in “Return of the Jedi.”)

Tarkin presented considerably greater difficulties, but the filmmakers said it would be just as hard to omit him from a narrative that prominently features the fearsome Death Star — the battle station he refuses to evacuate amid the rebels’ all-out assault in “Star Wars.”

“If he’s not in the movie, we’re going to have to explain why he’s not in the movie,” said Kiri Hart, a Lucasfilm story development executive and “Rogue One” co-producer. “This is kind of his thing.”

For principal photography, the filmmakers cast the English actor Guy Henry (“Harry Potter and the Deathly Hallows”), who has a build and stature like Cushing’s and could speak in a similar manner.

Throughout filming, Mr. Henry wore motion-capture materials on his head, so that his face could be replaced with a digital re-creation of Cushing’s piercing visage.

Mr. Knoll described the process as “a super high-tech and labor-intensive version of doing makeup.”

“We’re transforming the actor’s appearance to look like another character, but just using digital technology,” he said.

Image

Guy Henry was cast to play Tarkin in principal photography for “Rogue One.”

In striving for a balance between a digital figure who seemed real and one who looked precisely like Cushing, the “Rogue One” creators said seemingly minor tweaks could make significant differences — and these details were tinkered with constantly.

For example, the original “Star Wars” film (also known as “A New Hope”) was lit differently than “Rogue One,” raising questions of how to adjust the lighting on the character.

Hal Hickel, an Industrial Light & Magic animation supervisor, said that lighting him “the way he was in ‘A New Hope’ improved his likeness as Tarkin, but it worsened the sense of him being real because then he didn’t look like any of the actors in the scene.”

Side-by-side comparisons of Cushing’s daily footage from “Star Wars” and Mr. Henry’s motion-capture performance also called attention to subtle tics in the original actor’s delivery.

As Mr. Knoll explained, “When Peter Cushing makes an ‘aah’ sound, he doesn’t move his upper lip. He only opens his jaw about halfway, and makes this square shape with his lower lip, that exposes his lower teeth.”

Before nuances like this were accounted for, Mr. Knoll said their creation “looked like maybe a relative of Peter Cushing and not him exactly.”

Still, the animators had one golden rule: “Realism had to trump likeness,” Mr. Hickel said.

If the overall effect had not succeeded, Mr. Knoll said there were other narrative choices that would reduce Tarkin’s screen presence. “We did talk about Tarkin participating in conversations via hologram, or transferring that dialogue to other characters,” he said.

Lucasfilm and Industrial Light & Magic said their re-creation of Cushing was done with the approval of the actor’s estate. But the technique has drawn criticism from viewers and writers. The Huffington Post called it “a giant breach of respect for the dead,” and The Guardian said it worked “remarkably well” but nonetheless described it as “a digital indignity.”

Mr. Knoll said he and his colleagues were aware of the “slippery slope argument,” that their simulated Cushing was opening the door to more and more movies using digital reproductions of dead actors.

“I don’t imagine that happening,” Mr. Knoll said. “This was done for very solid and defendable story reasons. This is a character that is very important to telling this kind of story.”

He added: “It is extremely labor-intensive and expensive to do. I don’t imagine anybody engaging in this kind of thing in a casual manner.”

If “Star Wars” films are still made in 50 or 100 years, Mr. Knoll said audiences would probably not see likenesses of Mark Hamill or Harrison Ford playing Luke Skywalker or Han Solo. (He noted that the actor Alden Ehrenreich had already been cast to play the young Han Solo in a coming film about that character.)

Image

Carrie Fisher as Princess Leia in the original “Star Wars.”CreditLucasfilm

“We’re not planning on doing this digital re-creation extensively from now on,” Mr. Knoll said. “It just made sense for this particular movie.”

The filmmakers also pointed to a scene at the end of “Rogue One,” when the intercepted Death Star plans are delivered to Princess Leia — who has been digitally recreated to look like Carrie Fisher in the original “Star Wars” — as an appropriate and effective use of the technology. Ms. Fisher died on Tuesday.

In her first shot, when Leia is seen from behind (with her trademark hair buns), she is played by a flesh-and-blood actor, Ingvild Deila. Then, in the reverse angle, when Leia is seen from the front, her face, hair and costume are a digital re-creation of Ms. Fisher, based on footage from “A New Hope.” (The character’s extended hand is Ms. Deila’s.)

“To deliver on that moment of hopefulness, that is really underscored by the fact that you do get to see her face,” Ms. Hart said. “That’s the best possible use of effects, to enhance the meaning and the emotion of the experience for the viewer.”

The “Rogue One” filmmakers reviewed the dailies from “Star Wars” and turned up other Easter eggs to add to their movie. They included unused footage of the X-Wing fighter pilots known as Red Leader (Drewe Henley) and Gold Leader (Angus MacInnes), who help wage the rebels’ attack on the Death Star.

(Some of that original film, Mr. Knoll said, was “somewhat underexposed,” requiring some digital repair work. The actors were then transferred by rotoscope from that footage and inserted into computer-generated cockpits for “Rogue One.”)

Mr. Knoll said he did not come across a “vast gold mine” of footage that Mr. Lucas did not use. “George was pretty economical in the way he shot the films originally,” Mr. Knoll said. “When he was happy with a performance, he’d go, ‘All right — I got it.’”

But Mr. Knoll gained a greater appreciation for “Star Wars” by seeing brief scenes and snippets of dialogue left on the editing-room floor. One lost moment that Mr. Knoll described was a scene with Cushing and Ms. Fisher, after Princess Leia has seen Tarkin and his crew use the Death Star to destroy her home planet, Alderaan, and she bitterly responds, “And you call yourselves human.”

“It’s super fun, from a geeky fan point of view,” Mr. Knoll said. But, he added: “It’s a bit of a cheesy line. I totally understand why they cut that out.”

A version of this article appears in print on , on Page AR14 of the New York edition with the headline: Familiar Faces From a Long Time Ago. Order Reprints | Today’s Paper | Subscribe